1. Field of the Invention
The present invention relates to a substrate processing method for processing a substrate by a liquid.
2. Description of the Related Art
In a manufacturing process for a semiconductor device or a liquid crystal display, a substrate processing apparatus is used to process a substrate, such as a semiconductor wafer or a glass substrate for liquid crystal display, etc. A single substrate processing type substrate processing apparatus that processes a substrate one by one includes, for example, a spin chuck that rotates the substrate while holding the substrate horizontally and a processing liquid nozzle that supplies a processing liquid to an upper surface of the substrate held by the spin chuck.
In the processing of the substrate by the substrate processing apparatus, for example, the processing liquid is discharged from the processing liquid nozzle toward an upper surface central portion of the substrate in the rotating state. The processing liquid discharged from the processing liquid nozzle lands on the upper surface central portion of the substrate and instantly spreads toward an upper surface peripheral edge portion of the substrate upon receiving a centrifugal force due to rotation of the substrate. The processing liquid is thereby supplied to an entire upper surface of the substrate and the processing by the processing liquid is performed on the upper surface of the substrate. After the processing by the processing liquid has been performed, a drying processing (spin drying) of drying the substrate by rotating the substrate at high speed by means of the spin chuck is performed.
A substrate processing apparatus described in Japanese Patent Application Publication No. 2010-238758 includes a gas discharge nozzle having an annular upper gas discharge port, an annular lower gas discharge port, and a central gas discharge port. Each of the upper gas discharge port and the lower gas discharge port discharges nitrogen gas radially along a major surface of the substrate. Nitrogen gas flow passages that respectively communicate with the upper gas discharge port and the lower gas discharge port are in communication with each other and the nitrogen gas is thus discharged at the same time from the upper gas discharge port and the lower gas discharge port. The central discharge port faces the major surface of the substrate and discharges a weak nitrogen gas stream. The nitrogen gas stream changes direction at the major surface of the substrate to form a nitrogen gas stream parallel to the major surface of the substrate. The nitrogen gas discharged from the upper gas discharge port, the lower gas discharge port, and the central discharge port thus forms three layers of nitrogen gas streams that are parallel to the major surface of the substrate. The three layers of nitrogen gas streams prevent splashed-back liquid droplets and mist from becoming attached to a front surface of the substrate.
According to the prior art of Japanese Patent Application Publication No. 2010-238758, the nitrogen gas streams parallel to the major surface of the substrate are formed in a spin drying process of rotating the spin chuck at high speed. The removal of a liquid on the front surface of the substrate is mainly dependent on the centrifugal force due to the rotation of the substrate and the nitrogen gas streams do not have a practical effect on the removal of liquid. Although the weak nitrogen gas stream is discharged from the central discharge port toward the major surface of the substrate, it is weakened sufficiently in pressure so that a liquid film on the substrate will not be removed (see paragraph 0068 of Japanese Patent Application Publication No. 2010-238758).
In a typical substrate processing process, a chemical liquid is supplied to the substrate held by the spin chuck. Thereafter, a rinse liquid is supplied to the substrate and the chemical liquid on the substrate is thereby replaced by the rinse liquid. Thereafter, the spin drying process is performed to remove the rinse liquid on the substrate. In the spin drying process, the substrate is rotated at high speed to spin off and eliminate (dry) the rinse liquid attached to the substrate. A typical rinse liquid is deionized water.
If a fine pattern is formed on the front surface of the substrate, it may not be possible to eliminate the rinse liquid, which has entered into an interior of the pattern, by the spin drying process and this may cause drying failure to occur. Thus as described in Japanese Patent Application Publication No. 9-38595, a method is proposed where an organic solvent liquid, such as an isopropyl alcohol (IPA) liquid, etc., is supplied to a front surface of a substrate after processing by a rinse liquid to replace the rinse liquid, which has entered into an interior of a pattern, with the organic solvent liquid and thereby dry the front surface of the substrate.
As shown in FIG. 28, in the spin drying process of drying the substrate by high-speed rotation of the substrate, a liquid surface (an interface of air and liquid) is formed inside the pattern. In this case, surface tension of the liquid acts at positions of contact of the liquid surface and the pattern. The surface tension is one cause of collapse of the pattern.
If, as in Japanese Patent Application Publication No. 9-38595, an organic solvent liquid is supplied to the substrate before the spin drying process, the organic solvent liquid enters in between the pattern. The surface tension of an organic solvent is lower than that of water, which is a typical rinse liquid. The problem of pattern collapse due to surface tension is thus alleviated.
However, recently, patterns (projecting patterns, line-shaped patterns, etc.) that are fine and high in aspect ratio are being formed on front surfaces of substrates to achieve higher integration of devices (for example, semiconductor devices) prepared using substrate processing. A pattern that is fine and high in aspect ratio is low in strength and therefore collapse may be caused even by the surface tension that acts on an organic solvent liquid surface.
To resolve this issue, in Japanese Patent Application Publication No. 2014-112652, after forming a liquid film of an organic solvent on a front surface of a substrate, the substrate is heated to form a gas phase film of the organic solvent on an entire upper surface of the substrate. The organic solvent liquid film supported by the gas phase film is then removed. By the gas phase film being formed in between and above a fine pattern, a state is attained where a liquid surface of the organic solvent hardly contacts the fine pattern. The organic solvent liquid thus does not dry in a state of contacting the fine pattern and therefore the surface tension acting on the fine pattern is lightened significantly to enable suppression of fine pattern collapse.